Sinclair ZX80 / ZX81 / Z88 Forums

mrtinb wrote: ↑Fri Jan 03, 2020 7:02 am And again Mark’s invaluable help, knowledge and kindness to help.c

+1

Hi, and thanks everyone!!! The Minstrel is working. The answer was EPROM. So for some reason after a windoz update my programmer appeared to be working, but was running in a demo mode. After a day of soldering and stuffing I failed to notice that. It even looked like it was verifying the EPROM. I un...

Looking at the IORQ it appears to always stay low

I put a meter on the line to check for a ground, with the power off it reads in the megs. The connection between the cpu pin 20 and pin 5 of IC 19 is 0 ohms. So it is not open or shorted to ground.

What would cause the Z80 to keep that low?

It doesn’t look like it is following the normal run loop, as /IORQ never changes state. Definitely need to see A14 and A15 and A0 to A7... As the TV picture is entirely generated by the CPU executing the display file, with a little help from the hardware logic chips, if it is not running the normal...

Hi Len When you say the screen lights up, do you mean the display goes to a white colour (assuming a colour display)? If not, could you either take a photo or give a more detailed description. What signals do you get on the following pins of the Z80 CPU? Be very careful, if you short the probe betw...

Hi Ien, did you try out "grey border" jumper. Even if Processor is in reset state this should give a grey output, so shift register and things around that can be tested. If reset goes to high(check if it does) there should be some data seen in D0-D7. Next you may pull ram and eprom out of the board...

Ok, I spent some quality time with the Saleae this afternoon and this is what I am seeing. I'll go back and look at some of your suggestions after I post this up date. Looking at the main timing chain I am good: http://i8008.net/ZX81/Timing.JPG I chase things further down to the Draw_Character signa...

Ok, time to trouble shoot. All jumpers in and configured for NTSC. I have A13/14/15 high using a 27C64 EPROM burned with this: https://k1.spdns.de/Vintage/Sinclair/80/Sinclair%20ZX81/ROMs/zx81%20version%202%20'improved'%20rom%20(Sinclair).rom No obvious bent pins or bad solder joints. Top of board h...

Hi, I just soldered together my Minstrel 3 board today. I have a 27C64 that I need to burn the SW in. Two questions: 1. What ROM image do those who have built one suggest I use? 2. In the docs it is suggested that the jumper settings for A13/A14/A15 be set high. That puts the ROM image in the top 8k...

mrtinb wrote: ↑Tue Dec 10, 2019 6:39 am https://problemkaputt.de/zxdocs.htm

http://www.worldofspectrum.org/ZX81BasicProgramming/

Perfect! THanks Martin

len